Crystal oscillator circuit for adjusting resonant frequency of crystal oscillator

Abstract

A crystal oscillator includes a clock generator, first and second capacitors, a crystal oscillator, a variable capacitance diode, and a voltage generating circuit. The crystal oscillator is connected between the input pin and the output pin of the clock generator, and connected between the first terminal of the first capacitor and the first terminal of the second capacitor. The variable capacitance diode is connected between the second terminal of the first capacitor and the second terminal of the second capacitor. The voltage generating circuit is connected between two terminals of the variable capacitance diode to supply different voltages for the variable capacitance diode to change a junction capacitance of the variable capacitance diode, to change a resonant frequency of the crystal oscillator.

1 . A crystal oscillator circuit comprising:
 a clock generator comprising an input pin and an output pin;   a first capacitor comprising a first terminal and a second terminal;   a second capacitor comprising a first terminal and a second terminal;   a crystal oscillator connected between the input pin and the output pin of the clock generator, and connected between the first terminal of the first capacitor and the first terminal of the second capacitor;   a variable capacitance diode connected between the second terminal of the first capacitor and the second terminal of the second capacitor; and   a voltage generating circuit connected between two terminals of the variable capacitance diode, to supply different voltages for the variable capacitance diode to change a junction capacitance of the variable capacitance diode, thereby to change a resonant frequency of the crystal oscillator.   
     
     
         2 . The crystal oscillator circuit of  claim 1 , wherein the voltage generating circuit includes a direct current (DC) power supply and a voltage division circuit, the voltage division circuit is connected between the DC power supply and ground, to receive a voltage from the DC power supply to supply the different voltages for the variable capacitance diode. 
     
     
         3 . The crystal oscillator circuit of  claim 2 , wherein the voltage division circuit comprises a first resistor and a variable resistor, the first resistor is connected to the variable resistor in series between an anode of the DC power supply and ground, a cathode of the DC power supply is grounded, a cathode of the variable capacitance diode is connected to a node between the first resistor and the variable resistor to receive the different voltages from the voltage division circuit, an anode of the variable capacitance diode is connected to the cathode of the DC power supply, the junction capacitance of the variable capacitance diode increases with a voltage between the anode and cathode of the variable capacitance diode decreasing, the junction capacitance of the variable capacitance diode decreases with a voltage between the anode and cathode of the variable capacitance diode increasing. 
     
     
         4 . The crystal oscillator circuit of  claim 3 , wherein the voltage generating circuit further comprises a second resistor and a third resistor, the second resistor is connected between the cathode of the variable capacitance diode and the node between the first resistor and the variable resistor, the third resistor is connected between the anode of the variable capacitance diode and the cathode of the DC power supply. 
     
     
         5 . A crystal oscillator circuit comprising:
 a clock generator comprising an input pin and an output pin;   a crystal oscillator connected between the input pin and the output pin of the clock generator;   a first capacitor comprising a first terminal and a second terminal, the first terminal of the first capacitor connected to the input pin of the clock generator;   a second capacitor comprising a first terminal and a second terminal, the first terminal of the second capacitor connected to the output pin of the clock generator;   a variable capacitance diode connected between the second terminal of the first capacitor and the second terminal of the second capacitor; and   a voltage generating circuit connected in parallel to the variable capacitance diode, wherein when the voltage generating circuit voltage varies, the capacitance of the variable capacitance diode changes, thereby changing a resonant frequency of the crystal oscillator.